On the Fight screen and a Pokémon's summary it is called '-', because this name is used for no move (also hex:00) in situations where a Pokémon knows less than four moves, but it acts as a glitch move when it's forced as the first move.

Upon using it, and when a PP Up is applied to it, its name is taken from the memory and is essentially random.

Obtaining '-' as the first move

In Pokémon Red and Blue, the swapping Transform moves glitch can be used to put '-' in the first position of the moves list if the number of moves after the transformation is greater than the number of moves before the transformation.

Example 1: Ditto normally only knows Transform, so if it transforms into a Pokémon with four moves, swapping the second move with the first will make it have CoolTrainer♀ as the first move after the battle.

Example 2: A Mew knowing only three moves including Transform can encounter a Pokémon with four moves and transform into it. Then, swapping the fourth move with the first move will give CoolTrainer♀ as the first move after the battle.

The swapping Transform moves glitch was fixed in Pokémon Yellow, however, the player can still trade a Pokémon with an accessible '-' over from Pokémon Red and Blue.

Certain glitch Pokémon know the CoolTrainer♀ move as their first starting move, and many can learn the CoolTrainer♀ move through level up, meaning that the first move can be replaced with it if the Pokémon already has four moves.

0 initial PP and how to restore it

After obtaining '-' as the first move it may have 0/13 PP at first, and healing at a Pokémon Center won't restore its PP. However, if the player uses a certain PP restoring item (Ether or Max Ether only), it's possible to use the move.

Semi-Super Glitch effect

An effect similar to Super Glitch may be triggered with '-' when it is the first move by opening the fight menu or trying to move the cursor. After the effect occurs, the type of '-' may change from CoolTrainer♀ to another type.

Unlike other unterminated name/Super Glitch moves, only one buffer overflow occurs with '-' (at memory address $CF4B, but not $D0E1). No corruption is caused by the '-' move when viewing it from a status screen.

Triggering the Semi-Super Glitch with '-' requires more luck than other Super Glitch moves, so the player may need to keep 'moving' the cursor or opening and closing the fight menu. After a certain point in the player's game, CoolTrainer♀ induced corruption may stop working, due to hex:50 characters appearing in its internal name too early. There is no known guaranteed way to fix this other than to use a different cartridge.

The most basic effect that can be triggered with the CoolTrainer♀ move is the TMTRAINER effect, by opening the 'PkMn' menu from within battle before viewing it in the 'Fight' menu. Triggering the TMTRAINER effect in Diglett's Cave will let you avoid a freeze immediately after the battle ends. Opening the start menu after the TMTRAINER effect happens and the battle ends may be required to avoid a freeze after exiting the cave.

With the TMTRAINER effect, the enemy Pokémon's species will change into a level 127 Missingno. (hex:32) if sprites are not flipped, and a level 127 Horsea is obtainable by catching the enemy Pokémon if the sprites are flipped. Though the Pokémon's sprite will not change to the new Pokémon until it is captured, its palette may change to that of the new Pokémon.

Advanced Red/Blue usage

In Pokémon Red and Blue, more Pokémon can be obtained with '-' (and also Super Glitch) by viewing the Pokémon menu in specific places where there is a 0x50 sub-tile (often the 'bottom-left corner of a bush' tile) between y coordinates 09-0C (these are BGB coordinates; y starts as 00 at the top of the screen and increases the further down you go) before entering Diglett's Cave and triggering Semi-Super Glitch with '-'. Additionally the sub-tile at BGB coordinates y=06, x=01 must be equal to the desired Pokémon.

Keep in mind that the start menu is added to the saved screen data, and the west most tiles of the start menu are between x=0A-13, so the 50 tiles replaced with start menu tiles don't count.

Advanced Yellow usage

Despite the fact that 0x00 move corruption no longer works by directly bringing over tiles from outside of battle in this version, it is still possible to get the aforementioned Level 127 MissingNo. or Horsea by flashing the items menu in battle.

Additionally, using the Pokédex glitch item and closing it will print tiles on the screen in battle (but not in the same pattern as outside of battle), which can be used to potentially access CoolTrainers by flashing the items menu from within battle.